It's not abnormal for dogs to pant. Whether it's because it's a hot day or they're nervous about something like thunder, there are various and totally normal reasons why our furry friends might breathe a little heavier on occasion. Which makes it difficult to tell when it's normal and when it's something to be concerned about. Here are some reasons why dogs pant and ways to know if the panting is serious, according to WebMD.
If your dog is partaking in some heavy exercise, such as playing with you or another pet, it's normal for them to pant a bit. Dogs normally take between 10 and 30 breaths per minute (depending on the breed), so it's important to take notice just how hard they're really panting. If the panting goes on for longer than you'd expect, and often, it's a smart idea to get them checked out by your vet.
If it's particularly hot outside and your dog is panting, it's best to get them water and bring them inside. Dogs do not sweat like humans, and obviously cannot communicate to us with words. Panting is their way of telling you: Let's go back inside. When heat levels are extremely high, it's best to err on the safe side and keep them indoors entirely. And never, ever leave your dog in a hot car—even if it's "just for a minute."
Your pup's panting could also be the result of nervousness or stress. If you notice your dog excessively panting in the car, for example, it's nothing to get too worked up about. (It could very well be that simply being in the car makes them nervous.) Just make sure the area they're experiencing stress in is kept at a cool temperature, and that they have water nearby. If you know what situations can trigger anxiety in your dog—fireworks, for example—do your best to keep them away from these situations when at all possible.
Though there are all sorts of normal reasons why your dog might be panting, it can sometimes be indicative of a bigger issue. If you notice your pet excessively panting for no apparent reason, they might be sick. The list of possibilities of what could be wrong is is long and ranges from anywhere to allergies and respiratory disorders to heart failure or Cushing's syndrome.
If at any time your dog's panting cannot be explained, or somehow seems "off" to you, definitely take them to the vet ASAP. You know your dog's behaviors best, so if something doesn't seem right, it's best to consult with an expert.